KR100890770B1 - Catalyst - Google Patents

Abstract

Suitable catalysts for dehydrogenation and hydrogenation of hydrocarbons include at least one first metal and at least one second metal bonded to a support material. At least one first metal comprises at least one transition metal, suitably a platinum group metal. The support material has an overlayer so that acidic sites on the support material are substantially blocked. In a preferred embodiment, the catalyst is also substantially free of chloride. Also disclosed is a method of making a catalyst.

Hydrocarbons, dehydrogenation, hydrogenation, catalysts, support materials, transition metals, platinum groups.

Description

Catalyst {CATALYST}

The present invention relates to improved catalysts, and in particular to improved supported catalysts suitable for the dehydrogenation and hydrogenation of hydrocarbons, and methods for their preparation.

Among the known catalysts for dehydrogenation and hydrogenation of hydrocarbons, those prepared by supporting the platinum group metal (PGM) and group IV elements of the periodic table on high surface area metal oxide supports are most effective. It is important that the PGM and Group IV elements are well interdispersed on the support surface. This requires the use of a suitable precursor that is applied as a solution to the support before the resulting material is heat treated to form the active catalyst. Indeed, because of the low solubility and insufficient intercompatibility of many available precursors, the desired high interdispersity is difficult to achieve. Chloride salts are sometimes the only precursors actually used. However, the use of chloride salts exhibits a deleterious effect on the catalyst. Chloride ions on the support surface can cause the occurrence of undesirable reactions such as isomerization, carbon attachment and methane formation. High surface area supports often complicate the problem by containing incidental electron-accepting (acidic) species or sites that can exhibit deleterious effects such as chloride ions.

EP 0 166 359 discloses a process for dehydrogenation of a feedstock containing isobutane, n-butane and butadiene using a steam activated catalyst. Three types of catalysts are described, all of which are supported on highly calcined spinel supports. The first catalyst type is prepared by impregnating the support with a PGM solution, such as, for example, chloroplatinic acid; The second type of catalyst comprises further impregnation with a Group IA metal solution; And the third type adds further impregnation with tin, germanium or lead solutions. Chloride containing solutions are preferred. The impregnation process may be performed in any order or may be executed simultaneously.

EP 0 094 684 discloses a process of leaving metal only on the surface of a support by applying a noble metal catalyst to the support. This is said to be obtained by impregnating the support with a platinum sulfite complex. Preferred supports include zinc aluminate. The catalyst thus prepared is suitable for the dehydrogenation of butane.

In a first aspect of the invention, a catalyst suitable for dehydrogenation and hydrogenation of hydrocarbons comprises at least one first metal and at least one second metal bonded to a support material, and at least one first metal Comprises at least one transition metal; The support material has an overlayer such that the acidic sites on the support material are substantially blocked.

For example, blocking the acidic sites originally present on the surface of the metal oxide support improves the selectivity of the catalyst and reduces or substantially blocks the occurrence of unwanted side reactions. Acidic sites can “pyrolyze” hydrocarbons, producing unwanted methane, and also inducing the hydrocarbons to form aromatic molecules, which in turn can lead to rapid catalyst deactivation by forming carbon deposits on the catalyst. This process of catalyst deactivation is known as "caking".

In contrast, in EP 0 166 359, there is no specified order in which the components must be impregnated on the support. The formation of the overlayer is not taught and therefore will remain to allow acid sites on the support to interfere with the catalytic reaction.

In a preferred embodiment, the catalyst is substantially free of chloride.

The catalyst thus prepared minimizes the production of improved selectivity, unwanted reaction products. In addition to optimizing the yield of the desired product, improved selectivity reduces coking and leads to significantly increased catalyst life. One example of an advantageous process from the use of the catalyst according to the invention is to dehydrogenate ethane to obtain ethylene. Current state of the art supported PGM catalysts produce significantly higher amounts of unwanted methane than that of ethylene, whereas most of the product is ethylene when using the catalyst of the present invention. The substantial and economic advantages of the present invention are clear.

During the catalysis dehydrogenation and hydrogenation processes of hydrocarbons (eg EP 0 166 359), water vapor is added to inhibit carbon formation, otherwise the carbon formation becomes ineffective. Steam generation consumes energy, adding further cost and complexity to the process. A further advantage of the catalyst of the present invention is that no water vapor is required for this process.

In a second aspect of the invention, a process for preparing a catalyst suitable for dehydrogenation and hydrogenation of hydrocarbons                 

(a) contacting the support material with a solution of the overlayer precursor,

(b) drying and calcining the support material to form an overlayer,

(c) contacting the treated support material with a solution of at least one first metal precursor and at least one second metal precursor, and

(d) drying and calcining the treated support material to form a catalyst, the overlayer comprising a metal oxide that is more basic than the support material to substantially block acidic sites on the support material.

Preferably, the overlayer is more basic than the support material, and more preferably, the overlayer is substantially non acidic. Suitably, the overlayer comprises tin oxide, germanium oxide, lead oxide, copper oxide, zinc oxide, gallium oxide, lanthanum oxide, barium oxide or any mixture thereof. In a preferred embodiment, the overlayer comprises a tin oxide layer. The overlayer may be attached from the overlayer precursor solution, which may include any soluble salt of the desired metal. For example, a solution of SnCl ₂ 2H ₂ O in hydrochloric acid is suitable as an overlayer precursor for the formation of tin oxide overlayer. After immersion in the solution for about 2 hours, for example, the support material may be dried in air at 120 ° C. for about 8-12 hours and then calcined in air at about 500 ° C. for 4-8 hours. These process times and temperatures are not defined and may be changed as known to those skilled in the art without departing from the scope of the present invention.

It is known that platinum group metals are particularly effective at catalyzing the dehydrogenation and hydrogenation of hydrocarbons, preferably at least one primary metal is a transition metal selected from the group of platinum, palladium, rhodium, ruthenium, iridium and osmium It includes. Suitably, the at least one first metal precursor is a salt of platinum, palladium, rhodium, ruthenium, iridium or osmium.

Preferably, the at least one second metal is tin, but germanium, lead, gallium, copper, zinc, antimony and bismuth may also be used. Preferably, the at least one second metal precursor comprises salts of tin, germanium, lead, gallium, copper, zinc, antimony and bismuth, with salts of tin being particularly preferred.

In some embodiments of the invention, the second metal may be the same as used for forming the overlay. For example, tin oxide overlayer can be used with a second metal comprising tin. For example, it will be understood that the functions of the two sources of tin are separate. As described above, the overlayer blocks acidic sites on the support to prevent unwanted side reactions, while the second enhances the catalytic activity of transition metals such as, for example, platinum.

Attaching both the first metal and the second metal from the same solution together is the simplest because it requires fewer process steps. It is also advantageous if only a single solution is used, the interdispersion of the metal species is improved. If desired, respective solutions of each species can be used, but it is clear that the catalyst thus produced is less effective.

Preferably, the solution (or solutions) of at least one first metal precursor and at least one second metal precursor is free of chloride. More preferably, the at least one first metal precursor comprises an anionic carboxylate such as, for example, acetate, oxalate, or tartrate, and the at least one second metal precursor is selected from BF ₄ ⁻ . Contains anions.

In a particularly preferred embodiment, the solution of at least one first metal precursor and at least one second metal precursor comprises K ₂ [Pt (C ₂ O ₄ ) ₂ ] and Sn (BF ₄ ) ₂ in aqueous citric acid solution. Include.

BF ₄ ^- The use of results in the formation of BF ^- complex ions on the surface of the catalyst. These complex anions are believed to have the following beneficial effects during the hydrogen removal reaction and the hydrogen addition reaction.

(i) complex anions create an electronegative environment, promoting desorption of the desired product,

(ii) complex anions interfere with the occurrence of side reactions that lead to carbon attachment (caking) to the catalyst.

Preferably, the support material is an oxide, carbide or sulfide of a metal or silicon; carbon; Or any mixture or solid solution thereof. More preferably, the support material is at least one metal oxide selected from the group of alumina, spinel, silica, magnesia, toria, zirconia and titania. If desired, suitable oxides such as hydrotalcites can be obtained by thermal treatment of the minerals.

The support material may take any physical form, but finely divided forms are preferred to maximize the active surface area. In one embodiment, the support may be formed from a slurry and the slurry may be used as a washcoat to provide a catalyst coating to any suitable structure, such as, for example, bulk ceramics, metals or other solid structures.

If desired, the catalyst may further comprise a promoter. Suitable promoters include alkali metals such as lithium, sodium, potassium, rubidium and cesium. The promoter may be included in the catalyst by a separate process step, for example by treatment with an alkali metal salt, but preferably the promoter is included as a cation in at least one first metal precursor. For example, when K ₂ [Pt (C ₂ O ₄ ) ₂ ] is used as the first metal precursor, potassium is included as a promoter. In addition to further reducing the overall acidity of the catalyst, the presence of alkali metals as promoters can block sites on the metal surface that are active against undesirable side reactions.

The catalyst of the present invention is suitable for the hydrogenation and dehydrogenation of any hydrocarbon species. Some non-limiting examples include hydrogenation reactions such as for converting unsaturated hydrocarbons to less saturated or fully saturated hydrocarbons; And dehydrogenation reactions such as conversion of ethane to ethylene, conversion of propane to propylene, conversion of isobutane to isobutylene or conversion of ethylbenzene to styrene. The reactant hydrocarbons may be provided in pure form, treated with a diluent such as nitrogen or hydrogen, combined with air or oxygen, or by any method known in the art.

The present invention will now be described by way of examples.

(Example 1)

(Preparation of standard catalyst, not according to the present invention)

Impregnated γ-Al ₂ O ₃ with an aqueous complex formed by mixing a catalyst having a nominal composition (weight) of 1.5% Pt-1.5% Sn / Al ₂ O ₃ with an acidified solution of chloroplatinic acid and tin (II) chloride. By using the method disclosed by FC Wilhelm of US Pat. No. 3998900. The resulting material was dried (110 ° C .; in air; 24 hours) and calcined (500 ° C. in air; 2 hours).

(Example 2)

Preparation of Pt-Sn Catalyst with Tin Oxide Overlay on Spinel Support

10 g of a catalyst with a nominal composition 1.5% Pt-1.5% Sn / 7.5% Sn-MgAl ₂ O ₄ , (i) forming a magnesium aluminate spinel, (ii) attaching a tin oxide overlayer to the spinel, (iii) impregnated with Pt-Sn complex.

Specifically, _{17.95g Mg (N0 3) 2 .6H} 2 0 and 52.52g Al (NO _{3) 3} .9H ₂ 0 was dissolved in deionized water in 1dm ^3. The pH of the solution was adjusted to 10 by addition of aqueous NH ₄ OH. This resulted in the formation of a white precipitate, which was washed several times with hot deionized water to separate the precipitate and remove all residual traces of NH ₄ NO ₃ . The solid was dried in air at 120 ° C. for 8 hours and finally calcined in air at 800 ° C. for 16 hours. X-ray diffraction analysis of this solid content confirmed that MgAl ₂ O ₄ was formed. 1.5g SnCl ₂ . 2H ₂ O was dissolved in 6 cm ³ 0.1 M aqueous HCl at 0 ° C. and contacted with MgAl ₂ O ₄ for 2 hours. The material was dried in air at 120 ° C. for 8 hours and then calcined in air at 500 ° C. for 4 hours. 0.29 g SnCl ₂ H ₂ O was dissolved in 6 cm ³ 0.1 M aqueous HCl solution at 0 ° C. 0.38 g of chloroplatinic acid was added to the acidified SnCl ₂ .2H ₂ O and the solution showed a dark red color consistent with the formation of the [PtCl ₂ (SnCl ₃ ) ₂ ] ² -complex. Before drying in air at 120 ° C. for 8 hours, the solution was contacted with 7.5% Sn-MgAl ₂ O ₄ material for 2 hours. The final catalyst was obtained by calcination in air at 500 ° C. for 4 hours.

(Example 3)

Preparation of Chloride-Free Catalysts Containing Pt-Sn on Alumina Supports

A 5 g catalyst having a nominal composition 1.5% Pt-1.5% Sn / θ-Al ₂ O ₃ was converted into a low acid alumina (θ-Al ₂ O) by a Pt-Sn complex formed from a Pt-free and precursor-free chloride precursor _It was prepared by impregnation ₃ ).

Specifically, 5 g θ-Al ₂ O ₃ was dried at 300 ° C. in air and cooled to room temperature in a dryer to ensure complete emptying of the pore structure. 0.18 g K ₂ [Pt ^II (C ₂ 0 ₄ ) ₂ ] was added to 7 cm ³ 100 g1 ⁻¹ aqueous citric acid and warmed until the solution formed showed a lime green color.

0.38 g Sn (BF ₄ ) ₂ (50% aqueous solution) was added to this solution and a dark red color developed. The solution was left to cool to room temperature and contacted with the support for 2 hours, then dried in air overnight at 120 ° C. and finally calcined in air at 500 ° C. for 4 hours.

(Example 4)

Preparation of Chloride-Free Catalysts Containing Pt-Sn on a Spinel Support

A 5 g catalyst having a nominal composition 1.5% Pt-1.5% Sn / MgAl ₂ O ₄ was formed with magnesium aluminate spinel (as described in Example 2) and then chloride-free Pt (as described in Example 3). It was prepared by impregnation with -Sn complex. The impregnated spinel was dried in air at 120 ° C. for 8 hours and calcined in air at 500 ° C. for 4 hours.

(Example 5)                 

(Performance of catalyst)

The catalyst was tested using the ethane dehydrogenation process disclosed by BM Maunders and SR Partington of WO 9405608, wherein the dehydrogenation catalyst is combined with a hydrogen removal material. The presence of the hydrogen removal material is in the forward (dehydrogen) and reverse (re- When the reaction is allowed to equilibrate, it is generally intended to increase the yield of ethylene above the value reached.

In each test, 1 g of catalyst was mixed with 3 g hydrogen-removing material. The mixture was charged to a cylindrical reactor and heated to 500 ° C. An undiluted stream of ethane (20 cm ³ min ^-1 ) was passed through the reactor for 2 minutes, and all the exhaust gases were collected and analyzed. The process was repeated until the hydrogen storage material was saturated and ethylene yield was returned to the normal equilibrium value (3.7% at 500 ° C.). The hydrogen storage material could be regenerated by passing air through the reactor.

Table 1 shows the molar conversion of ethane, the molar selectivity to ethylene and the molar yield of ethylene for each of the catalysts (Examples 2 to 4) according to the invention and for the conventional catalysts (Example 1). The values are averages based on two minute exposures to ethane each, both before saturation and after regeneration. In all cases, ethylene yields exceeded general equilibrium yields. The conventional catalyst (Example 1) is the most active in terms of% conversion, but was consumed by converting most of the ethane to methane. Each preparation according to the invention exhibited substantially high selectivity for ethylene and the most selective catalyst was a catalyst prepared by impregnating a low acid support material with a chloride free Pt-Sn complex (Example 3). .

Ethane dehydrogenation catalyst transform % Selectivity% Ethylene Yield% Ethylene Example 1 (Prior Art) 49 11 5.5 Example 2 26 71 18 Example 3 25 80 20 Example 4 19 84 16

(Example 6)

(Catalyst with lanthanum oxide overlayer)

A standard catalyst (not according to the invention) with the nominal composition 1% Pt-1% Sn / Al ₂ O ₃ was prepared according to Example 1. Further catalysts according to the invention were also prepared in a similar manner, except that an alumina support with La ₂ O ₃ attached to form an overlayer was used. The nominal composition of this catalyst was 1% Pt-1% Sn / 10% La ₂ O ₃ / Al ₂ O ₃ . After impregnation, the catalyst was dried in air at 100 ° C. for 24 hours and then calcined in air at 500 ° C. for 2 hours.

Both catalysts were tested using the oxidative dehydrogenation process of alkanes initiated by SE Golunski and JW Hayes of EP 0638534 B1. Isobutane (50 cm ³ min ⁻¹ ) was passed through a cylindrical reactor at a temperature of 500 ° C. and 0.5 g of catalyst was charged. When the catalyst bed temperature began to drop, at the start of dehydrogenation, only sufficient air was added to isobutane to achieve thermally neutral operation (ie bed temperature = gas inlet temperature).

After 2 minutes of oxidative dehydrogenation, at the first measurement, the yield of isobutene was the same for both the standard catalyst and the catalyst with La ₂ 0 ₃ overlayer (30%). However, the rate of subsequent deactivation was higher for standard catalysts. It took 90 minutes for the isobutene yield to drop from 30% to 20% for the standard catalyst. However, the catalyst with La ₂ 0 ₃ overlayer took twice as long to deactivate in the same amount.

Claims (16)

At least one first metal and at least one second metal bonded to the support material, wherein the at least one first metal is selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium and osmium At least one transition metal; The at least one second metal is selected from the group consisting of tin, germanium, lead, gallium, copper, zinc, antimony and bismuth; Wherein said support material comprises an overlayer comprising a layer of tin oxide, germanium oxide, lead oxide, zinc oxide, gallium oxide, lanthanum oxide, barium oxide or any mixture thereof. The catalyst of claim 1 wherein the catalyst is free of chloride. delete delete 3. The method of claim 1 or 2, wherein the support material comprises an oxide, carbide or sulfide of a metal or silicon; carbon; Or at least one of any mixture or solid solution thereof. 6. The catalyst of claim 5 wherein the support material comprises at least one selected from the group consisting of alumina, spinel, silica, magnesia, toria, zirconia and titania. The catalyst according to claim 1 or 2, further comprising a promoter. 8. The catalyst of claim 7 wherein the promoter comprises an alkali metal. (a) contacting the support material with a solution of the overlayer precursor, (b) drying and calcining the support material to form an overlayer, (c) contacting the calcined support material with a solution of at least one first metal precursor and at least one second metal precursor, and (d) drying and calcining the treated support material to form a catalyst, wherein the overlayer comprises a metal oxide that is more basic than the support material; The metal oxide is selected from tin oxide, germanium oxide, lead oxide, zinc oxide, gallium oxide, lanthanum oxide, barium oxide and mixtures thereof; The at least one first metal precursor comprises a salt of platinum, palladium, rhodium, ruthenium, iridium or osmium; Wherein said at least one second metal precursor comprises a salt of tin, germanium, lead, gallium, copper, zinc, antimony or bismuth. delete 10. The method of claim 9, wherein the at least one first metal precursor comprises an anionic carboxylate. The method of claim 9, wherein the at least one second metal precursor comprises an anion of BF ₄ ⁻ . The method of claim 12, wherein the solution of at least one first metal precursor and at least one second metal precursor comprises K ₂ [Pt (C ₂ O ₄ ) ₂ ] and Sn (BF ₄ ) ₂ in an aqueous citric acid solution. Method comprising a. delete A method of hydrogenating or dehydrogenating a hydrocarbon comprising contacting the hydrocarbon with the catalyst of claim 1. delete